1. Field of the Invention
The present invention relates to an electrophotographic apparatus that may be realized in the form of a relatively small light-emitting diode (LED) printer or the like.
2. Description of the Related Art
FIG. 68 is a schematic view illustrating construction of an electrophotographic apparatus 501 typical of the prior art. The electrophotographic apparatus 501 comprises a lower housing 502 of box-like shape having an open top and an upper housing 503 having an open bottom. A paper cassette 504 is installed in one side of the lower housing 502, with a portion of the paper cassette 504 extending outwardly of the lower housing 502. A recording paper delivered from the paper cassette 504 is transported through the electrophotographic apparatus 501 in a transporting direction indicated by arrow A1. The terms "upstream" and "downstream" are used in a relative sense in relation to the recording paper transporting direction indicated by arrow A1, unless otherwise noted. The upper housing 503 is swingably joined to the lower housing 502 by means of a shaft 514 near the lower end portion of the upper housing 503 at the downstream end of the transporting direction A1. In the upstream side of the upper housing 503, there is detachably installed a process cartridge 510 that contains a charge unit 506 for uniformly charging a photoconductor drum 505, a developing device 508 for forming a toner image on the photoconductor drum 505 on which an electrostatic latent image has been formed by the illumination of light from an optical head 507, and a cleaning device 509 for removing residual toner on the photoconductor drum 505 after transfer. The optical head 507 forms a desired optical image on the charged photoconductor drum 505.
In the lower housing 502, downstream of the paper cassette 504 and below the photoconductor drum 505, are disposed a transfer device 511 for transferring a toner image on the photoconductor drum 505 onto a recording paper fed from the paper cassette 504, a guide 512 for guiding the recording paper after transfer, and a fixing device 513 for fixing the toner image to the recording paper. The recording paper with the toner image fixed thereon passes an inverting member 515, through which its travelling direction is inverted, and is discharged onto a stacker 516 mounted on the upper housing 503.
The process cartridge 510 is detachably mounted to the underside of the upper housing 503. When the toner contained in the developing device 508 has run out, for example, the upper housing 503 is opened by turning it about the shaft 514, the process cartridge 510 is removed from the underside of the upper housing 503, and a new process cartridge 510 is installed in place. After that, the upper housing 503 is closed. The electrophotographic apparatus 501 thus becomes ready for use.
The electrophotographic apparatus 501 of the above prior art has various problems as enumerated below.
(1) As described, the upper housing 503 is connected to the lower housing 502 by means of the shaft 514 provided near the lower end of the upper housing 503 at the downstream end of the transporting direction A1. With this construction, when the upper housing 503 is opened, the upper housing 503 protrudes outwardly from the downstream end of the electrophotographic apparatus 501, as shown by two-dot chain lines in FIG. 68. The resulting problem is an increased space requirement for installation since the protrusion of the upper housing 503 must be taken into consideration when securing the installation space for the electrophotographic apparatus 501.
(2) The process cartridge 510 is mounted on the underside of the upper housing 503. Therefore, removal of the process cartridge 510 or installation of a new process cartridge 510 has to be performed in the narrow space positioned very close to the upper housing 503. This reduces work efficiency for removal and installation of the process cartridge 510.
FIG. 69 is a schematic view further illustrating the construction of the electrophotographic apparatus 501 shown in FIG. 68. A recording paper fed from the paper cassette 504 by means of a paper feed roller 520, is transported by transport rollers 521 through guides 522 and 525, and is carried between resist rollers 523 through a guide 524 to reach the transfer device 511. The recording paper with a toner image transferred thereon by the transfer device 511 is directed along a guide 512 to the fixing device 513 where the toner image is fixed by heat, etc. After fixing, the recording paper is passed along a guide 528, and discharged outside the apparatus by means of paper discharge rollers 530, or stacked on the stacker 516 shown in FIG. 68, if necessary.
In the electrophotographic apparatus 501 of FIG. 69, the guides, 524 and 512, and the transfer device 511 are the components used to support the recording paper during the process from the time the recording paper is delivered from the resist rollers 523 for transfer, until it is delivered to the fixing device 513 for fixing. These components are separately mounted to the housing, etc. of the electrophotographic apparatus 501.
However, in the above prior art arrangement, the provision of the various components between the resist rollers 523 and the fixing device 513 increases the complexity of the entire construction. Furthermore, separate structures are required to mount the guides 524 and 512 and the transfer device 511 to the housing, etc. of the electrophotographic apparatus 501, which presents the problem of further increasing the complexity of the construction.
Also, the electrophotographic apparatus 501 of the above prior art employs a construction that enables the apparatus to be opened along the recording paper transport path into two sections, the upper and lower sections, to expose the transport path. This construction is employed to facilitate removal of the recording paper when the recording paper is jammed during a printing operation. FIG. 70 is a schematic view showing the upper housing 503 turned upward around the shaft 514 relative to the lower housing 502 on which the upper housing 503 is swingably supported. In this condition, the recording paper transport path is exposed so that a jammed paper can be removed easily.
Furthermore, in the electrophotographic apparatus 501 of the above prior art arrangement, the developing device 508 is detachably mounted into the apparatus body to facilitate developer replenishment and parts replacement operations. Besides such construction, the photoconductor drum and the cleaning unit are often constructed as an integral unit for detachable mounting on the apparatus. In the apparatus of such construction, however, the developer tends to fall through openings, etc. of the developing device 508. This tendency is particularly noticeable when a shock is applied to the apparatus or the unit, for example, when removing the developing device 508 from the apparatus for replacement or when opening or closing the upper housing. As a result, the falling developer is scattered over the paper transport path upstream of the photoconductor drum, that is, over the guide 522. If the guide 522 is contaminated with toner, the toner adheres to the recording paper during the printing operation, resulting in degradation of the print quality.
The developing device 508 includes a developing roller 531 and a toner box 532 for supplying toner for development to the developing roller 531. The toner in the toner box 532 is distributed downward by the rotation of a toner supply roller 534 disposed adjacent to a toner supply port 533. The falling toner is carried by a toner moving member 535 and moved toward an agitator 536 which mixes the toner with carrier. The toner moving member 535 is formed, for example, from a plate-like member, and is rotated to move the toner.
However, in the above prior art electrophotographic apparatus 501, the toner moving member 535 in the developing device 508 is a plate-like member that only works to push the toner toward the agitator 536. The toner is therefore not scattered over the agitator 536, which presents a problem in terms of toner/carrier mixing efficiency.
Furthermore, in the developing device 508, carrier formed from filings of ferromagnetic material is stored in a space 537 that also houses therein the developing roller 531 to which toner is supplied from the toner box 532. The carrier with toner adhering thereto is made to adhere to the circumference of the developing roller 531, forming a so-called magnetic brush and thereby applying toner to the photoconductor drum 505.
To seal the carrier in the developing device 508, a sleeve is mounted on the shaft of the developing roller 531, and the sleeve is used as a slide bearing for supporting the shaft installed through the housing of the developing device 508. Transmission of power to the developing device 508 is achieved by rotating the developing roller 531 via a gear or the like mounted on a portion of the shaft extending outwardly from the housing of the developing device 508. Therefore, carrier and toner tend to leak from the developing device 508, which may result in contamination of the interior of the electrophotographic apparatus 501 that uses the developing device 508 of such construction, and hence the contamination of the recording paper travelling therethrough. This may also lead to the problem of soiling the hands and fingers of the operator when handling the developing device 508. On the other hand, if the developing device 508 is to be hermetically sealed, the construction of the bearing for the shaft will become complex.
In the electrophotographic apparatus 501 of FIG. 68, a waste toner box 538 for storing waste toner removed by the cleaning device 509 from the photoconductor drum 505 is accommodated in the lower housing 502, not in the process cartridge 510. That is, when the upper housing 503 is closed around the lower housing 502, the process cartridge 510, in particular, the cleaning device 509, becomes connected to the waste toner box 538 so that the waste toner removed by the cleaning device 509 is collected into the waste toner box. This construction allows the continued use of the process cartridge 510 just by replacing the waste toner box 538.
The above construction, however, has the problem that, each time the upper housing 503 is opened to expose the lower housing 502 for maintenance of the process cartridge 510 or for removal of jammed paper in the electrophotographic apparatus 501, the joint between the cleaning device 509 and the waste toner box 538 is opened, causing toner to spill over the interior of the electrophotographic apparatus 501.
To solve such a problem, the process cartridge 510 may be constructed to include a built-in waste toner box. This, however, introduces certain problems of its own. One is that the size of the process cartridge has to be increased to accommodate the waster toner box. Another is that the service life of the process cartridge becomes short as it has to be discarded when the waste toner box becomes fully loaded with waste toner.
As shown in the perspective view of FIG. 71, the upper housing 503 comprises a rectangular top plate part 539 and rectangular side plate parts 540, 541 extending downward from both widthwise ends of the top plate part 539 toward the lower housing 502, the width of the top plate part 539 being taken orthogonal to the transporting direction A1. At the lower ends of the side plate parts 540 and 541 are formed stop pieces 542 and 543 extending toward each other. Protrusions 544 and 545 are formed on the opposing inner surfaces of the side plate parts 540 and 541. The lower end faces of the protrusions 544 and 545, i.e., the faces thereof facing the stop pieces 542 and 543, are formed to match the shape of the upper surface of the process cartridge 510. These faces are formed as stop faces 546 and 547 curving closer to the stop pieces 542 and 543 with decreasing distance from the shaft 514.
That is, when the process cartridge 510 is mounted into the upper housing 503, side parts 510a and 510b at both widthwise ends of the process cartridge 510 are held from above by the stop faces 546 and 547 and from below by the stop pieces 542 and 543 so that the process cartridge 510 can be positioned inside the upper housing 503, with a predetermined distance maintained from the transfer device 511 and without any play in vertical directions relative to the upper housing 503. Furthermore, the horizontal positioning of the process cartridge 510 is achieved by the side parts 510a and 510b thereof abutting the inside surfaces of the upper housing 503.
In the above prior art arrangement, the process cartridge 510 is mounted into the upper housing 503 of the above construction so that the process cartridge 510 can be held in position without any play either in vertical or width directions. However, when determining the dimensions of the outer shape of the process cartridge 510, the intervals of the inner surfaces of the side plate parts 540, 541 and the intervals between the stop faces 546, 547 and the stop pieces 542, 543, there must be clearance to such extent as to allow the process cartridge 510 to move inside the upper housing 503 in order that the process cartridge 510 can be detachably mounted into the upper housing 503.
This inevitably introduces certain play of the process cartridge 510 in the vertical and width directions when mounted in the upper housing 503. The play in the vertical direction will affect the quality of the image produced by transferring a toner image on the photoconductor drum onto the recording paper, and the play in the width direction will cause the image produced on the recording paper to be displaced widthwise thereof. Such image formation problems will become particularly noticeable when, for example, a plurality of toner images are superimposed to print an image on a single recording paper. The play in the width direction may also cause problems in transportation of the recording paper delivered from the paper cassette 504.
FIG. 72 is a perspective view showing a housing construction of the electrophotographic apparatus 501 of the typical prior art arrangement shown in FIG. 68. The electrophotographic apparatus 501 includes a lower housing 502 having an open top 550 and upper housing 503 covering the open top 550 of the lower housing 502. The upper housing 503 is swingably joined to the lower housing 502 by means of a pinned connection. In the lower housing 502, a pair of stop levers 551, 552 spaced apart from each other and rising toward the open top 550 are fixed on a shaft 553. The stop levers 551 and 552 are provided at their respective ends with stop pawls 551a and 552a extending toward the open top 550. Adjacent to the stop levers 551 and 552 are torsion springs 554 and 555 wound around the shaft 553. Respective ends of the torsion springs 554 and 555 abut spring stop pieces 551b and 552b provided on the stop levers 551 and 552, respectively, from sides thereof opposite from the sides facing toward the open top 550. Opposite ends of the torsion springs 554 and 555 are fixed to the lower housing 502, so that the torsion springs 554 and 555 urge the stop levers 551 and 552 in the direction of arrows D1. The shaft 553 is rotatably supported in both sides of the lower housing 502.
An upper end portion of the stop lever 552 extends in a direction opposite to the direction of the stop pawls 552a, and is swingably joined to a driving member 556 by means of a pinned connection. An upper end of the driving member 556 protrudes upward from an upper end face 502a of the lower housing 502 so that the operator can hold the protruding portion and move it in the direction of arrow D2. On the other hand, the upper housing 503 is provided with a pair of rod members 559, 560 supported by respective pairs of brackets 557, 558 at positions opposite the stop pawls 551a, 552a of the stop levers 551, 552 when the upper housing 503 is closed to cover the lower housing 502. The upper ends of the stop pawls 551a and 552a of the stop levers 551 and 552 are formed as sloping faces 561 and 562 sloping gradually downward away from the upper housing 503.
According to the above construction, when the upper housing 503 is turned to close the lower housing 502 of the electrophotographic apparatus 501, the rod members 559 and 560 hit the sloping faces 561 and 562 of the stop levers 551 and 552, causing the stop levers 551 and 552 to turn in the direction opposite to the direction of arrow D1 against the spring forces of the torsion springs 554 and 555. When the upper housing 503 is further turned downward, the stop pawls 551a and 552a are engaged into respective spaces between the upper housing and the rod members 559, 560, respectively, thereby locking the upper housing in position with respect to the lower housing 502.
On the other hand, to release the upper housing 503 from the lower housing 502, the driving member 556 is moved in the arrow direction D2 to turn the stop levers 551 and 552 in the direction opposite to the direction of arrows D1. This causes the stop pawls 551a and 552a to disengage from the rod members 559 and 560, so that the upper housing 503 can be turned upward and opened.
However, in the above electrophotographic apparatus 501, the integral construction incorporating the stop levers 551, 552 and torsion springs 554, 555 requires the extra operation of fixing the stop levers 551, 552 onto the shaft 553 by caulking, for example, as well as the construction that permits such operation. It also requires the use of torsion springs 554, 555 that are different parts from the stop levers 551, 552. Thus the above prior art arrangement has the problems of increasing the complexity of the construction and the number of components as well as the number of production steps. Such prior art arrangement has the further problem that the sloping faces 561, 562 and the stop levers 551, 552 abutting them can easily wear.
Furthermore, in the prior art electrophotographic apparatus 501 of FIG. 69, the transport rollers 521, the upper guide 525, the lower guide 522, and the resist rollers 523, which together constitute a transport device, are separately fixed to the housing of the electrophotographic apparatus 501. Therefore, when a paper jam has occurred in the vicinity of the transport rollers 521 or between the upper and lower guides 525 and 522 or near the resist rollers 523, the transport rollers 521 or the resist rollers 523 have to be rotated by hand to remove the jammed paper. When the jammed paper is lying between the upper and lower guides 525 and 522, an appropriate tool has to be used to remove the paper. Such manner of paper removal is cumbersome and labor consuming.
One approach to solving this problem is by constructing the housing in two separate sections, the upper housing and the lower housing, one being swingably joined to the other at one end thereof. In such construction, the photoconductor drum, developing unit, etc. are mounted inside the upper housing, and when the upper housing is opened, the transport device is exposed. Further, the upper guide 525 is swingably joined to the lower guide 522. However, this construction has the problem that if it is attempted to close the upper housing of the electrophotographic apparatus 501 with the upper guide 525 left open relative to the lower guide 522, the inside of the upper housing hits against the end of the upper guide 525 and may damage important parts, such as the photoconductor drum, developing device, etc., held inside the upper housing,
FIG. 73 is a perspective view showing a paper exit section in the electrophotographic apparatus 501 of the typical prior art arrangement shown in FIG. 68. The electrophotographic apparatus 501 includes the rectangular box-like housing 503 in which inverting member 515 for changing the paper travelling direction upward and redirecting the paper toward the upstream side of the transporting direction A1, is provided near the downstream end of the transporting direction A1. The recording paper passed through the inverting member 515 is discharged onto a recording paper collection part 580 formed on the upper surface of the housing 503. Adjacent to the entrance to the inverting member 515 is a shaft 572 rotatably supported between side plate parts 570 and 571 of the housing 503. A plurality of driving rollers 573 spaced apart from each other by a prescribed distance are fixed on the shaft 572. Arranged upwardly of the driving rollers 573 in contacting relationship thereto are driven rollers 574. The driving rollers 573 and the driven rollers 574 constitute pairs of paper discharge rollers 530.
Each driven roller 574 has a shaft 581 that extends axially outward from both axial ends thereof in parallel to the axis of the shaft 572. The shaft 581 extending axially outward from both axial ends of each driven roller 574 is rotatably mounted to a mounting member 575, fixed from the rear side thereof, in the vicinity of an end part 503a of the housing 503 at the downstream end of the transporting direction A1.
The mounting member 575 is fixed at an end thereof to the end part 503a of the housing 503 and includes a connecting part 575a extending upstream from the end part 503a along the transporting direction A1, and support pieces 575b, 575c extending downward from both widthwise ends of the connecting part 575a. The shaft 581 is rotatably supported on the support pieces 575b, 575c.
Furthermore, there is provided for each driven roller 574 a plate spring 576 which, with a spring force thereof, presses down the shaft 581 from above as viewed facing FIG. 73. The plate spring 576 is essentially U-shaped in plan view, and includes a rectangular plate-like connecting part 577 fixed to the end part 503a and extending in parallel to the transporting direction A1, and a pair of pressure parts 578 and 579 extending from both widthwise ends of the connecting part 577 toward the downstream side of the transporting direction A1 and pressing downward the portions of the shaft 581 protruding from both axial ends of each driven roller 574. A plate spring 576 of such construction is provided for each of the driven rollers 574.
The paper discharge rollers 530 of the above prior art arrangement operate as follows. When the recording paper has reached the transporting direction A1 area after transfer, the recording paper is guided and caught between the driving rollers 573 and the driven rollers 574. The recording paper is further transported downstream along the transporting direction A1 by the rotation of the driving rollers 573. At this time, the pressure parts 578, 579 of each plate spring 576 press the shaft 581 downward with their spring force, and at the same time, are bent in the thickness direction thereof according to the thickness of the recording paper, thereby allowing vertical displacement of each driven roller 574.
When, for example, a relatively small-sized and stiff paper such as a post card is fed between the paper discharge rollers 530 of the above prior art arrangement, the post card will pass between one or two pairs of paper discharge rollers 530 near the widthwise center of the housing. After that, the travelling direction of the post card will be turned 180 degrees by passing along the inverting member 515. However, at this time, the leading edge of the post card may be bent upward along the inverting member 515 when the trailing edge thereof has not yet exited the paper discharge rollers 530. If this happens, since the post card is relatively stiff, there is a possibility that the driven roller 574 that should hold down the post card may be displaced upward by the post card against the spring force of the plate spring 576 and may not be able to sufficiently press the post card onto the driving roller 573. In this case, the rotation of the driving roller 573 cannot be transmitted to the driven roller 574, causing the post card to stop partway through the inverting path.
Furthermore, in an electrophotographic apparatus of typical prior art construction comprising a cleaning device for removing toner remaining on the surface of a photoconductor drum, and a waste toner container for collecting waste toner discharged from the cleaning device, there is provided a shutter at a waste toner exhaust port to prevent the waste toner from spilling out of the cleaning device when the cleaning device and the waste toner container are separated each other in an operation of exchanging the cleaning device or the waste toner container.
FIGS. 74(a)-74(c) are schematic cross-sectional view showing the shutter mechanism of the waste toner exhaust port of such prior art. As shown in FIG. 74 (a), on part of the cleaning device is mounted a cylindrical waste toner transport member 594 provided with a waste toner exhaust port opening downward. A shutter 593 which can cover the waste toner exhaust port and slide around the outer circumference of the waste toner transport member 594 prevents the waste toner 595 inside from leaking out.
In this condition, when waste toner container 591 provided with an opening 592 is moving rightward in FIG. 74(b), first a corner portion 591a of the waste toner container 591 comes in contact with a lever 593a integrated with the shutter 593. As the waste toner container 591 is further moving rightward, the shutter 593 is displaced angularly in the counterclockwise direction as shown in FIG. 74 (b), until the opening 592 takes a position just under the waste toner exhaust port as shown in FIG. 74 (c) and the waste toner falls down by its own weight out of the waste toner exhaust port.
Thus, most of the waste toner 595 accommodated inside the waste toner transport member 594 can be collected into the waste toner container 591.
According to another prior art shutter mechanism, there is provided a protrusion on a portion of the housing frame which can open and close relatively to the electrophotographic apparatus body upon the housing frame closing, such protrusion engaging a shutter mounted at the waste toner exhaust port and opening or closing the shutter.
However, in the prior art shutter mechanism shown in FIGS. 74(a)-74(c), the arrangement that the lever 593a of the shutter 593 and the waste toner container 591 come in contact directly is likely to bring about a restriction on the order of the attaching/detaching operation of the cleaning device provided with shutter 593 and the attaching/detaching operation of the waste toner container 591. Therefore, there are difficulties of operation that one is not attachable if the other is not attached to the electrophotographic apparatus body.
Furthermore, as shown in FIG. 74 (b), since there exists a state that the shutter 593 is gradually opening in the process of the attaching operation of the waste toner container 591, a part of the waste toner 595 is likely to leak out of the opening of the shutter 593 until the waste toner container 591 takes a regular position, resulting in the problem that all of the waste toner 595 cannot be collected into the waste toner container 591 and a part thereof may be scattered.
On the other hand, in such prior art arrangement, whether the waste toner container is set in the electrophotographic apparatus body or not, the opening / closing operation of the housing frame causes the shutter to open, resulting in the problem that a portion of the waste toner is likely to be scattered inside the apparatus in case the housing frame closes without attaching the waste toner container.